One of the complications of obesity is the development of insulin resistance leading to type 2 diabetes. Recent studies have implicated alterations in mitochondrial function in the pathogenesis of insulin resistance. Whether this is a primary cause of insulin resistance or is secondary to other changes has not been determined. To date no human subject with a fatty acid oxidation (FAO) disorder, inherited defects in mitochondrial FAO, has been reported to develop insulin-resistance or diabetes. The FAO pathway is an essential mitochondrial process involved in energy production. Our current study, K01 DK071869 Fatty Acid Oxidation Disorders and Body Weight Regulation, is investigating insulin resistance in humans with long-chain FAO disorders and we now propose to examine this relationship in a murine model of very long-chain acylCoA dehydrogenase deficiency (VLCADD). We hypothesize that mice with a homozygous deletion of the VLCAD gene will accumulate long-chain acylcarnitines and cytosolic lipid intermediates but will not develop diet-induced insulin resistance compared to wild-type littermates. To test this hypothesis, we will compare lipid deposition in tissues (including ceramide, and diacylglycerols), acylcarnitines, and ketones, markers of mitochondrial function and oxidative stress, and insulin sensitivity by hyperinsulinemic euglycemic clamp studies in VLCAD-/- and wild-type littermates fed either high-fat or standard mouse chow for 12 weeks. Data from these experiments will help define the relationship between FAO and the development of diet-induced insulin resistance. If our hypothesis is true, future grant applications will propose studies to extend the findings by selectively restoring VLCAD activity in insulin sensitive tissues to examining the molecular mechanisms for the protection against diet-induced insulin resistance. PUBLIC HEALTH RELEVANCE: One of the complications of obesity is the development of insulin resistance leading to type 2 diabetes. Humans with inherited defects in mitochondrial fatty acid oxidation (FAO) such as very long-chain acylCoA dehydrogenase deficiency (VLCADD) have not been reported to develop insulin-resistance or diabetes. We propose to test the hypothesis that a block in the FAO pathway prevents the development of diet-induced insulin resistance in a murine model of VLCADD.